Research On Key Technology Of MIMO In Visible Light Communication Systems

With the development of industry 4.0,virtual reality,stereo holographic map,etc.,the scarcity of Radio Frequency(RF)spectrum resource congestion is increasingly prominent.Under this background,visible light communication(VLC),which uses high-frequency visible light waves to transmit information,has attracted the attention of the industry and academia.Besides,multiple-input multiple-output(MIMO)technologies can effectively enhance the data rate and link stability of VLC systems.Thus,MIMO VLC is considered as one of the potential enabling technologies to meet the high peak rate and new capability indicators of future mobile communication,which has application prospects in shortdistance communication,indoor positioning and navigation,transportation communication,etc.The research of the doctoral dissertation is supported by the project of the National Natural Science Foundation of China "Spatial dimming theorems and techniques in visible light communications"(Project Number:61871047).Focusing on the existing issues in MIMO VLC research,such as difficulty to balance flexible dimming and high-speed communication,difficulty to balance illuminance uniformity and communication reliability,strong spatial correlation of channels limits the capacity,and the high complexity of channel estimation and precoding in mobile scenarios,this doctoral dissertation proposes a series of solutions.The main research work and innovations are as follows:First,a generalized spatial dimming(GSD)technology based on multi-domain index modulation is investigated to balance flexible dimming and high-speed communication.To solve the issue that the activation ratio of light-emitting diodes(LEDs)and the amplitude range of modulated signals are limited at a given illumination level,a GSD scheme based on spatial-time index modulation(GSD-STIM)is proposed,which can enhance the diversity of transmitted symbols by joint spatial and temporal domain modulation and improve the energy efficiency of the system by transmitting additional information through the active index of space-time signal matrix.To further improve the spectral efficiency of the system,a GSD scheme based on spatial-frequency index modulation(GSD-SFIM)is proposed,in which optical orthogonal frequency division multiplexing(O-OFDM)is used to improve the anti-multipath ability and spectrum efficiency of the system.Moreover,the joint spatial and frequency domain modulation technique is investigated to reduce the peakto-average ratio of O-OFDM signals and improve the effective signal-tonoise ratio(SNR)of the system.Then,adaptive spatial dimming(ASD)technology with illuminance uniformity is investigated to balance illuminance uniformity and communication reliability.First,based on the GSD-STIM scheme,an ASD scheme based on activation mode selection(ASD-AMS)is proposed,in which an incremental index mapping algorithm is proposed to optimize the activation mode of the spatial-time signal matrix to ensure that the activation probability of each LED is approximately equal.In addition,since the layout of LEDs is another important factor affecting the communication performance and illuminance uniformity of the system,an ASD scheme based on antenna layout(ASD-AL)is proposed.In ASD-AL,an antenna layout algorithm is designed under the dual constraints of illuminance uniformity and communication reliability,and thus it can enhance communication reliability while satisfying the uniformity of illumination of the system.Moreover,to solve the issue that the strong spatial correlation of channels limits the capacity,ordered QR precoding combined with SIC detection(OQR-SIC)technology under intensive LED deployment scenarios is investigated.In OQR-SIC,the OQR precoding is used to preprocess transmitted signals at the transmitter,while the SIC detection algorithm is used to detect received signals at the receiver.The OQR-SIC scheme can effectively alleviate the high complexity of sorting and error propagation in SIC detection.Finally,to solve the issue that the high complexity of channel estimation and precoding in mobile scenarios,SIC-based precoding with dynamic LED sub-array(SIC-DLS)with dynamic CSI is investigated,in which task-based quantization algorithm for channel estimation(TQ-CE)and SIC-DLS algorithm are proposed.Based on the vector quantization(VQ)algorithm and the minimize mean square error criterion,TQ-CE can obtain a more accurate estimated CSI with fewer quantization feedback bits.In SIC-DLS,each LED sub-array containing multiple LEDs is connected to a baseband chain to reduce the number of baseband chains required by the system.To further enhance the data rate of the MIMO VLC system,the LED sub-array structure,precoding matrix,electric power allocation and DC bias are jointly optimized.